Process for treatment of volcanic igneous rocks to recover gold, silver and platinum

Abstract

The recovery of gold, silver and platinum group metals from volcanic cinders containing iron is achieved by mixing the cinders with a suitable flux, and metallic copper, and smelting the mixture at a sufficiently high temperature to produce a molten mass of metal containing iron and copper, and a molten slag. The molten slag is separated from the molten metal mass by a suitable means. The slag is discarded and the metal mixture is cooled to a solid state. The copper and iron are then dissolved in acid, leaving an undissolved portion which can then be separated from the resulting leach liquor by filtration. Alternatively, the iron and copper bearing metal can be cast into an anode and electrolyzed in a sulfuric acid solution where copper is deposited at the cathode and iron is put into solution as iron sulfate. The insoluble residue at the anode can be recovered from the sulfuric acid solution by filtration. The filtered solids from either acid dissolution or electrolysis contain a significant amount of the gold, silver, and platinum group metals that were present in the original ore. These solids can then be processed by well known technology to recover their gold, silver, and platinum group metal content in essentially pure form. The solution which contains most of the silver can be treated by conventional means to recover that metal. With electrolysis copper is recovered as a cathode deposit. With acid dissolution copper can be recovered by other conventional methods. With either method copper can be recycled to the process.

I claim: 
     
       1. A method for treating iron-bearing igneous ores for the recovery of gold, silver and platinum group metal values contained in such ores by: mixing an iron-bearing igneous ore containing gold, silver, and platinum group metal values with a suitable flux and copper to form a mixture of ore, flux and copper;   heating the mixture of ore, flux and copper to a sufficiently high temperature to produce a molten mass of metal containing copper, iron, gold, silver and platinum group metal values, and a molten slag;   allowing the molten mass containing copper, iron, gold, silver and platinum group metal values, and slag to settle into a least two layers, so that the molten mass containing copper, iron, gold, silver and platinum group metal values forms a lower molten layer, and the slag forms an upper molten layer;   separating the upper and lower molten layers;   cooling the lower molten layer;   leaching the lower molten layer containing iron, copper, gold, silver and platinum group metal values with a dilute mineral acid to solubilize the iron, copper and most silver values in the presence of increased temperatures of up to about 80 degrees centigrade to form a solubilized iron, copper and silver leachate; leaving an undissolved residue containing gold, some silver and platinum group metal values;   separating the undissolved residue containing gold, some silver and platinum group metal values from the solubilized iron, copper and silver values leachate;   treating the undissolved residue containing gold, some silver and platinum group metal values to recover the gold, silver and platinum group metal values therefrom; and   treating the iron, copper and silver values leachate to recover the silver values from the leachate.   
     
     
       2. A method for heating volcanic cinders containing iron, gold, silver and platinum group metal values for the recovery of gold, silver and platinum group metal values therefrom, by: mixing iron-bearing volcanic cinders containing gold, silver and platinum group metal values with a suitable flux and copper to form a mixture of volcanic cinders, flux and copper;   heating the mixture of volcanic cinders, flux and copper to a sufficiently high temperature to produce a molten mass of metal containing copper, iron, gold, silver and platinum group metal values, and a molten slag;   allowing the molten mass containing copper, iron, gold, silver and platinum group metal values, and slag to settle into a least two layers, so that the molten mass containing copper, iron, gold, silver and platinum group metal values forms a lower molten layer, and the slag forms an upper molten layer;   separating the upper and lower molten layers;   cooling the lower molten layer;   leaching the lower molten layer containing iron, copper, gold, silver and platinum group metal values with a dilute mineral acid to solubilize the iron, copper and most silver values in the presence of increased temperatures of up to about 80 degrees centigrade to form a solubilized iron, copper and silver leachate; leaving an undissolved residue containing gold, some silver and platinum group metal values;   separating the undissolved residue containing gold, some silver and platinum group metal values from the solubilized iron, copper and silver values leachate;   treating the undissolved residue containing gold, some silver and platinum group metal values to recover the gold, silver and platinum group metal values therefrom; and   treating the iron, copper and silver values leachate to recover the silver values from the leachate.